Optimize visible_parent_map to use LRC to prevent unnecessary cloning

Author: In-line

compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -360,7 +360,7 @@ pub fn provide(providers: &mut Providers) {
                 visible_parent_map.entry(child).or_insert(parent);
             }
 
-            visible_parent_map
+            Lrc::new(visible_parent_map)
         },
 
         dependency_formats: |tcx, ()| Lrc::new(crate::dependency_format::calculate(tcx)),

compiler/rustc_middle/src/query/mod.rs

@@ -1552,7 +1552,7 @@ rustc_queries! {
         desc { "calculating the missing lang items in a crate" }
         separate_provide_extern
     }
-    query visible_parent_map(_: ()) -> DefIdMap<DefId> {
+    query visible_parent_map(_: ()) -> Lrc<DefIdMap<DefId>> {
         storage(ArenaCacheSelector<'tcx>)
         desc { "calculating the visible parent map" }
     }